docs: remove use of the term 'enslaved' wrt tap & bridge devices

Network interfaces are simply attached to a bridge device.
Reviewed-by: NPeter Krempa <pkrempa@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

docs/firewall.html.in

@@ -12,7 +12,7 @@
       <li>The virtual network driver
           <br /><br />
           This provides an isolated bridge device (ie no physical NICs
-          enslaved). Guest TAP devices are attached to this bridge.
+          attached). Guest TAP devices are attached to this bridge.
           Guests can talk to each other and the host, and optionally the
           wider world.
           <br /><br />
@@ -46,7 +46,7 @@
     </p>
     <p>Thus the virtual network driver in libvirt was invented. This takes
        the form of an isolated bridge device (ie one with no physical NICs
-       enslaved). The TAP devices associated with the guest NICs are attached
+       attached). The TAP devices associated with the guest NICs are attached
        to the bridge device. This immediately allows guests on a single host
        to talk to each other and to the host OS (modulo host IPtables rules).
     </p>

docs/formatdomain.html.in

@@ -5785,11 +5785,11 @@
     <p>
       Provides a bridge from the VM directly to the LAN. This assumes
       there is a bridge device on the host which has one or more of the hosts
-      physical NICs enslaved. The guest VM will have an associated tun device
+      physical NICs attached. The guest VM will have an associated tun device
       created with a name of vnetN, which can also be overridden with the
       &lt;target&gt; element (see
       <a href="#elementsNICSTargetOverride">overriding the target element</a>).
-      The tun device will be enslaved to the bridge. The IP range / network
+      The tun device will be attached to the bridge. The IP range / network
       configuration is whatever is used on the LAN. This provides the guest VM
       full incoming &amp; outgoing net access just like a physical machine.
     </p>